Process for preparing 1,5-diaryl-3-substituted pyrazoles

ABSTRACT

A process for making a compound of formula I wherein the substituents are as described in the specification comprising reacting a ketone of formula II with succinic anhydride and an alkoxide base to form a compound of formula III                    
     which is reacted with a compound of formula IV to form a compound of V                    
     and reacting with an alcohol to form the corresponding ester of formula VI                    
     and reacting the ester with N-methylhydroxylamine.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the continuation application of U.S. applicationSer. No. 09/629,997, filed Aug. 1, 2000, now abandoned, whichapplication claims the benefit U.S. Provisional application Ser. No.60/146,997, filed on Aug. 3, 1999.

BACKGROUND OF THE INVENTION FIELD OF THE INVENTION

The invention relates to a process of preparing 1,5-diaryl-3-substitutedpyrazoles of the formula

wherein

R₁, R₂, R₃ and R₄ are the same or different and are individuallyselected from the group consisting of hydrogen, lower alkyl, loweralkoxy, amino, acetamido, phenyl, halo, hydroxy, lower alkylsulfonyl,lower alkylthio, nitro, trifluoromethyl, omega-trifluoromethyl loweralkoxy, or where R₁, R₂ or R₃, R₄ taken together with the phenyl groupto which they are attached, form a naphthyl or substituted naphthylgroup.

In a preferred embodiment, the invention relates to a process of making5-(4-chlorophenyl)-N-hydroxy-1-(4-methoxyphenyl)-N-methyl-1H-pyrazole-3-propanamide,a compound of formula Ia, known as tepoxalin.

The compounds of formula I and method of making and using the compoundsof formula I are described in U.S. Pat. No. 4,826,868, issued May 2,1989, incorporated by reference herein.

Tepoxalin is a potent inhibitor of both the cyclooxygenase andlipoxygenase pathways of the arachidonic acid cascade (U.S. Pat. No.4,826,868 and Robinson, C., Drugs of the Future, 15, 9. 902 (1990)).

Known methods of synthesizing tepoxalin include the following. U.S. Pat.No. 4,826,868 describes reacting the alcohol,5-(4-chlorophenyl)-1-(4-methoxyphenyl)-1H-pyrazole-3-propanol with Jonesreagent to form the acid,5-(4-chlorophenyl)-1-(4-methoxyphenyl)-1H-pyrazole-3-propanoic acid,which is reacted with dimethylformamide and oxalyl chloride intetrahydrofuran (“THF”) which is then reacted with methylhydroxylaminehydrochloride and triethylamine in THF.

U.S. Pat. No. 4,898,952 describes a process for making tepoxalin whichcomprises reacting a hydrazine with a diketoacid to form a pyrazole acidwhich is reacted with dimethylformamide and oxalyl chloride to yield thepyrazole acid chloride which is reacted with methyl hydroxylaminehydrochloride and triethylamine to yield tepoxalin. The diketoacid isprepared by adding an appropriately substituted acetophenone to asolution of lithium diisopropylamide (LDA made from diisopropylamine andn-butyllithium in THF at low temperature). Alternatively, lithiumhexamethyl disilazide may be employed as the base in place of lithiumdiisopropylamide. Succinic anhydride is then added to this solution toproduce the diketoacid.

U.S. Pat. No. 5,117,054 describes a process wherein p-chloroacetophenoneis reacted with succinic anhydride to form4-chloro-γ,ε-dioxo-benzenehexanoic acid which is reacted with aceticanhydride or acetyl chloride to yield5-[2-(4-chlorophenyl)-2-oxoethylidene]dihydro-2(3H)-furanone. Thiscompound is then added to a mixture of N-methylhydroxylaminehydrochloride and an amine base such as triethylamine, Hunig's base,pyridine or lutidine and a solvent such as methylene chloride orchloroform to form4-chloro-N-hydroxy-N-methyl-γ,ε-dioxo-benzenehexanamide which iscombined with 4-methoxyphenyl hydrazine hydrochloride, an amine base asdescribed above in an alcoholic solvent such as methanol, ethanol orpropanol.

The preparation of 4-chloro-γ,ε-dioxo-benzenehexanoic acid fromp-chloroacetophenone utilizing various bases selected from lithiumdiisopropylamide (LDA); LDA.LiCl; magnesium diisopropylamide (MDA);MDA.lLiBr; MDA.2LiBR or lithium bis (trimethylsilyl) amide was disclosedin Murray et al, Synthesis 1991, p. 18-20.

Due to cost, toxicity, and hazard considerations, it is desirable to beable to synthesize 1,5-diaryl-3-substituted pyrazoles, particularlytepoxalin, without the reagents lithium hexamethyl disilazide, oxalylchloride and methylene chloride and without excess p-chloroacetophenone.

The current invention produces tepoxalin in a much higher over-all yieldand at a decreased cost than the known processes.

BRIEF SUMMARY OF THE INVENTION

The invention relates to a process for preparing a compound of theformula I

wherein

R₁, R₂, R₃ and R₄ are the same or different and are individuallyselected from the group consisting of hydrogen, lower alkyl, loweralkoxy, amino, acetamido, phenyl, halo, hydroxy, lower alkylsulfonyl,lower alkylthio, nitro, trifluoromethyl, omega-trifluoromethyl loweralkoxy, or where R₁, R₂ or R₃, R₄ taken together with the phenyl groupto which they are attached, form a naphthyl or substituted naphthylgroup;

comprising reacting a compound of formula II

wherein R₃ and R₄ are as described above, with succinic anhydride and analkoxide base to form the corresponding compound of formula III

wherein R₃ and R₄ are as described above, which is reacted with acompound of formula IV

wherein R₁ and R₂ are as described above, to form a correspondingcompound of formula V

wherein R₁, R₂, R₃ and R₄ are as described above, reacting the compoundof formula V with an alcohol to form the corresponding ester of formulaVI

wherein R₁, R₂, R₃ and R₄ are as described above and R is lower alkyl orcycloalkyl, and reacting the ester of formula VI withN-methylhydroxylamine hydrochloride and a base to form the correspondingcompound of formula I.

DETAILED DESCRIPTION OF THE INVENTION

In the above formula, R₁, R₂, R₃ and R₄ are substituents on phenylrings, where phenyl rings substitute for hydrogen atoms at positions 1and 5 of the pyrazole ring. It is preferred that at least one of R₁ andR₂, and one of R₃ and R₄ be substituted at the 4-positions of theirrespective phenyl rings.

Lower aklyl radicals include, for example, methyl, ethyl, propyl,isopropyl, n-butyl, sec-butyl, t-butyl, n-pentyl, 2-methyl-3-butyl,1-methylbutyl, 2-methylbutyl, neopentyl, n-hexyl, 1-methylpentyl,3-methylpentyl, 1-ethylbutyl, 2-ethylbutyl, 2-hexyl, 3-hexyl, octyl andthe like.

Lower alkoxy shall mean oxygen ethers formed from a before-describedlower alkyl group. Exemplary radicals include methoxy, ethoxy, propoxy,isopropoxy, n-butoxy, and the like.

Lower alkylthio radicals of R₁, R₂, R₃ and R₄ are thio ethers and arethus analogous to the ethers described above.

Halo radicals preferably include chloro and bromo, as well as fluoro andiodo.

Lower alkylsulfonyl radicals contain a before-described lower alkylradical bonded to an SO₂ moiety that is itself also bonded to a phenylring. Exemplary lower alkylsulfonyl radicals thus includemethylsulfonyl, ethylsulfonyl, 2-ethylbutylsulfonyl and the like.

An omega-trifluoromethyl lower alkoxy radical is a lower alkoxy radicalas before described that additionally includes a trifluoromethyl groupat a position farthest on the alkyl chain from the place of bonding tothe phenyl ring. Exemplary of such radicals are the2,2,2-trifluoroethoxy.

Naphthyl and substituted naphthyl radicals can replace an aryl groupherein at either the 1- or 2-positions to provide 1-naphthyl or2-naphththyl substituents respectfully. Substituents on the naphthylradicals can be any of those described herein as being useful arylsubstituents. Exemplary substituted 1- and 2-naphthyls include6-methoxy-2-naphthyl and the like.

As used herein, unless otherwise noted, the term “lower” when used withalkyl or alkoxy means a carbon chain composition of 1-6 carbon atoms.

The term “alkoxide base” refers to a lower primary alkoxide, secondaryalkoxide, or tertiary alkoxide such as, methoxide, ethoxide,2-propoxide, tert-butoxide and the like. The preferred base is atertiary alkoxide and preferably potassium tert-butoxide.

The invention relates to a process of preparing a compound of theformula I

comprising reacting a compound of formula II

with succinic anhydride and an alkoxide base to form a correspondingcompound of formula III

which is reacted with a compound of formula IV

to form a corresponding compound of formula V

reacting the compound of formula V with an alcohol to form thecorresponding ester of formula VI

wherein R is lower alkyl, such as methyl, ethyl, isopropyl, preferablyethyl, or aryl, and reacting the ester of formula VI withN-methylhydroxylamine hydrochloride and an appropriate base, such as analkoxide base, amine base or inorganic base such as NaOH or KOH,preferred is sodium ethoxide in ethanol, to form the correspondingcompound of formula I.

In a preferred embodiment, the invention relates to a process of makingcompound of formula I wherein

R₁, R₂ R₃, R₄ 4-OEt 4-Cl 3,4-diOMe 4-Cl 2-OMe 4-Cl 4-OMe 4-Me 4-Cl 4-OMe4-OMe 4-OMe 4-OMe 4-H 4-OMe 3-Me 4-OMe 3,4-diMe 4-OMe 2,4,6-tri-Me 4-OMe2-Me 4-OMe 4-Et 4-OMe 4-CF₃ 4-OMe 4-Cl 4-OMe 4-F 4-H 4-Cl

In a particularly preferred embodiment, the invention relates to aprocess of making tepoxalin (Ia), wherein R₁ is 4-OMe and R₃ is 4-Cl, R₂is H and R₄ is H.

As set forth in Scheme 1, a compound of formula II, a known compound orcompound prepared by known methods, is reacted with succinic anhydrideand an alkoxide base such as Li, Na, or K tert-alkoxide, preferablyK-tert-alkoxide, in a polar aprotic solvent such as dimethylformamide,(DMF) or THF, preferably DMF, preferably at an initial temperature fromabout −5 to 20° C., more preferably at 0-5° C., particularly preferredat 0° C., then heating to a temperature of 45-50° C. preferably at 45°C. to form the corresponding compound of formula III.

Preferably, 1 equivalent each of a compound of formula II, and succinicanhydride is reacted with 2 equivalents of an alkoxide base.

The compound of formula III is treated with, a compound of formula IV, aknown compound or compound prepared by known methods, or preferably itsHCl salt and a base such as KHCO₃, NaHCO₃, KOH, or NaOH, preferablyNaHCO₃, in a lower alcohol solvent such as methanol, ethanol, or2-propanol, preferably methanol, preferably at a temperature of fromabout 45 to 55° C., to form the corresponding compound of formula V. Thecompound of formula V is isolated by known methods preferably filtrationto remove NaCl, seeding and cooling of the filtrate, and filtration toisolate the compound of formula V.

The compound of formula V is reacted in an alcohol solvent such asmethanol, ethanol, 2-propanol, or benzyl alcohol, preferably ethanol,with a catalytic amount of an acid, such as sulfuric acid, hydrochloricacid, or p-toluene sulfonic acid at reflux temperature to produce thecorresponding ester of formula VI (methyl, ethyl, isopropyl, or benzylwith ethyl being preferred).

The ester of formula VI is isolated by conventional means such asconcentration, seeding, and filtration of the resulting solid. The esterof formula VI is treated with N-methylhydroxylamine hydrochloride (as asolid or as an alcoholic solution which has been prepared from anaqueous solution)and a base such as sodium methoxide, sodium ethoxide,sodium benzyl oxide or, sodium isopropoxide (preferably sodium ethoxide)or N-methyl hydroxylamine free base (a known compound) in an alcoholic.solvent such as methanol, ethanol, 2-propanol, or benzyl alcohol(preferably ethanol)to form the product of formula I. The product isisolated by known methods, preferably aqueous quench followed byfiltration.

Alternatively, the ester of formula VI is not isolated. In this case,the compound of formula V is treated with an alcohol such as methanol,ethanol, isopropanol, or benzyl alcohol, preferably ethanol, and acatalytic amount of an acid such as sulfuric acid, hydrochloric acid, orp-toluene sulfonic acid and heated to reflux to form the ester offormula VI and the reaction cooled. The resulting solution of the esterof formula VI is reacted directly with N-methylhydroxylaminehydrochloride (as a solid or as an alcoholic solution which has beenprepared from an aqueous solution) and basified with an appropriate basesuch as sodium methoxide, sodium ethoxide, sodium benzyl oxide or,sodium isopropoxide, preferably sodium ethoxide, to produce the productof formula I. The product is isolated by known methods, preferablyaqueous quench followed by filtration.

Alternatively, neither the acid of formula V or the ester of formula VIis isolated, and the compound of formula III is converted (withoutisolation of V or VI) to product of formula I. In this case, thecompound of formula III is treated with a compound of formula IV, aknown compound or compound prepared by known methods, or preferably itsHCl salt and a base such as KHCO₃, NaHCO₃, KOH, or NaOH, preferablyNaOH, in a lower alcohol solvent such as MeOH, EtOH, or 2-propanol,preferably ethanol, preferably at a temperature of from about 20 to 55°C. (preferably at ambient temperature, approximately 25° C.) to form thecorresponding compound of formula V. The resulting mixture of thecompound of formula V is then treated with an acid, such as sulfuricacid, hydrochloric acid, or p-toluene sulfonic acid and heated to refluxto produce the corresponding ester of formula VI. The resulting reactionmixture of the ester of formula VI is then treated directly withN-methylhydroxylamine hydrochloride (as a solid or as an alcoholicsolution which has been prepared from an aqueous solution) and basifiedwith an appropriate base such as sodium methoxide, sodium ethoxide,sodium benzyl oxide or, sodium isopropoxide, preferably sodium ethoxide,to produce the corresponding product of formula I. The product isisolated by known methods, preferably aqueous quench followed byfiltration.

In another embodiment, the claimed invention relates to a process ofmaking an intermediate of formula III

comprising reacting a compound of formula II with succinic anhydride inan alkoxide base.

In addition, the claimed invention relates to a process for preparing1,5-diaryl-3-substituted pyrazoles of formula I, particularly tepoxalin,comprising reacting a compound of formula V with an alcohol to form thecorresponding ester of formula VI (where for example R=Me, Et, iPr,preferably Et) and reacting the corresponding ester of formula VI withN-methylhydroxylamine hydrochloride.

This invention also relates to the novel intermediate of formula VI(where for example R is methyl, ethyl or isopropyl preferably ethyl).

The following examples describe the invention in greater detail and areintended to illustrate the invention, but not to limit it.

EXAMPLE 1

Potassium tert-butoxide (112.2 g 1 mol) was dissolved in DMF (250 mL)and cooled to 0° C. under a nitrogen atmosphere. p-chloroacetophenone(77.3 g, 0.5 mol) in DMF (50 mL) was added at 0° C. over about 30 minthen stirred at 0° C. for 30 min. Succinic anhydride (50.0 g. 0.5 mol)was dissolved in DMF (170 mL) at room temperature (heating may be neededto dissolve succinic anhydride in DMF. The solution should be cooled toroom temperature before it is added to the enolate solution) and wasadded to the above enolate solution at 0-5° C. over 80 min. The reactionmixture was stirred at 0-5° C. for 25 min, then heated to 55° C. for 30min. The reaction mixture was quenched by adding water (400 mL) withoutexternal cooling; final temperature was about 52-55° C. Immediatelyfollowing the quench, the reaction mixture was acidified to pH 5 withconc. HCl; final temperature was about 55-56° C. The reaction mixturebecame a light brown cloudy solution. The mixture was stirred and cooledto 5-10° C. The yellow solid product started forming at about 30° C. Theresulting yellow solid was collected by filtration and washed with water(300 mL). After most of the water was drained, the solid was washed withtoluene (250 mL) to remove any residual p-chloroacetophenone and most ofthe color. The solid was air-dried overnight. Yield: 68.8 g (53%).

EXAMPLE 2

5-(4-chlorophenyl)-1-(4-methoxyphenyl)-1H-pyrazole-3-propanoic acid (300g, 840 mmol) and ethanol (3 L) were placed in a flask. ConcentratedH₂SO₄ (2.4 mL, 86.4 meq.) was added with stirring. The reaction was thenheated to reflux. After approximately 30 minutes, the suspensiondissolved. The reaction was monitored by TLC (silica gel;hexane:ethylacetate:methanol;70:20:10). After refluxing for 9 hours, allstarting material was gone and 2 liters of ethanol was removed bydistillation. The remaining solution was cooled with stirring to 0° C.and seeded with knownethyl-5-(4-chlorophenyl)-1-(4-methoxyphenyl)-1H-pyrazole-3-propanoate.The resulting suspension was stirred at 0° C. for 30 minutes and thenfiltered, washed with cold ethanol (100 mL) and vacuum dried (roomtemperature, ca. 5 mm Hg) to giveethyl-5-(4-chlorophenyl)-1-(4-methoxyphenyl)-1H-pyrazole-3-propanoate(275.0 g, 85% yield) as a clean white powder (mp=80-81° C.). Anadditional 27.9 g ofethyl-5-(4-chlorophenyl)-1-(4-methoxyphenyl)-1H-pyrazole-3-propanoatewas obtained as a tan powder after reducing the volume of the motherliquor to approximately 100 mL and seeding with knownethyl-5-(4-chlorophenyl)-1-(4-methoxyphenyl)-1H-pyrazole-3-propanoate.

EXAMPLE 3

a) An oven-dried 1000 mL 3-necked round bottomed flask was equipped withan oven dried magnetic stirring bar, argon inlet, drying tube,thermometer, and an oven-dried 250 mL addition funnel. The flask wascooled to room temperature while supplying a stream of dry argon. Theflask was charged with dry ethanol (160 mL) (200 proof undenaturedethanol dried with 4 A molecular sieves was used) via the additionfunnel, and N-methylhydroxylamine hydrochloride (16.3 gm; 0.195 mole)was added to the stirring solvent to produce a clear colorless solution.The resulting mixture was cooled with an ice-water bath (1.0° C.) withstirring, and the addition funnel was charged with NaOEt (21 wt %, 170mL; 0.46 mole). All of the NaOEt was added drop-wise to the cooledstirring solution of N-methylhydroxylamine hydrochloride over a 30minute period (NaCl precipitated during the course of the addition, andthe temperature rose to 6.0° C.). After stirring the resulting slurryapproximately 15 minutes, the ethyl ester(ethyl-5-(4-chlorophenyl)-1-(4-methoxyphenyl)-1H-pyrazole-3-propanoate)(50.0 gm; 0.13 mole) was added with good stirring. The resulting mixturewas allowed to stir approximately 10 minutes, and then the reaction wasallowed to warm to ambient temperature. The reaction was monitored byTLC (10% MeOH in CH₂Cl₂ for product, 50% EtOAc in hexane for startingmaterial).

b) The reaction was allowed to stir for 16 hrs. The magnetic stirringbar was removed, and the flask was equipped with a mechanical stirrerand a 500 mL addition funnel. The reaction was cooled (2.5° C.) using anice-water bath. The addition funnel was charged with a cooled (ice-waterbath) mixture of glacial acetic acid (15 mL; 0.26 mole) and 330 mL ofdistilled water. The aqueous acetic acid mixture was added drop-wise tothe reaction mixture with good stirring over a 30 minute period. Thetemperature rose to 7.8° C. during the course of the aqueous quench.After the addition of 155 mL of the aqueous acetic acid mixture, thereaction mixture turned into a clear brown solution. Product began toprecipitate out slowly during the rest of the addition of the aqueousacetic acid mixture, and continued stirring and cooling after completionof the addition resulted in precipitation of more material. The pH atthe end of the quench was between 6.4-6.8 as determined by litmus paper.The resulting milky brown mixture was stirred with continued coolingfrom the ice-water bath to allow full precipitation of the solidproduct. The ice-water bath was removed. The ethanol was removed fromthe reaction by distillation under vacuum (80 mm Hg) with heating up to34.4° C. using a warm water bath. The mixture was cooled with anice-water bath, and the pH was adjusted from 6.0 to between 6.4-6.8 withthe addition of 21 mL of 1N NaOH. The resulting mixture was stirred 30minutes with cooling from the ice-water bath, and the product wasisolated by filtration through a course rated sintered glass funnel. Theisolated solids were washed with ice-cold distilled water (2×75 mL). Theproduct was air dried and then placed in a vacuum oven at 60° C. for14.5 hours to provide crude tepoxalin as a light tan solid (48.38 gm;96.5% yield).

c) A 1000 mL round bottomed 3-necked flask was equipped with amechanical stirrer, condenser, and thermometer. The flask was chargedwith crude tepoxalin (48.18 gm; 0.125 mole) and 190 mL of ethyl acetate.The mixture was heated to reflux with good stirring to produce an ambersolution. The solution was filtered hot through celite into another 1000mL flask (product crystalized out upon cooling during filtration). Thefiltrate was heated to reflux to produce a clear amber solution. Thesolution was cooled to ambient temperature with stirring to bring aboutcrystallization. After stirring 2 hrs at ambient temperature, themixture was cooled using an ice-water bath and stirred for 3 hrs. Themixture was filtered, and the collected solids were washed with ice-coldethyl acetate (2×50 mL). The product was air dried, and placed in avacuum oven. The product was dried in the vacuum at 60° C. for 15 hrs toprovide final product (45.08 gm; 89.9% yield, >99% HPLC wt % purity).

EXAMPLE 4

a) An oven dried 300 mL 3-necked round bottomed flask was equipped witha magnetic stirring bar, argon inlet, and drying tube. The flask wascharged with5-(4-chlorophenyl)-1-(4-methoxyphenyl)-1H-pyrazole-3-propanoic acid (10gm, 28.03 mmol) followed by ethanol (100 mL). The resulting solution wascooled using an ice-water bath, the stirring solution was treated withconcentrated H₂SO₄ (0.07 mL, 2.52 meq.). The flask was then removed fromthe ice-water bath, the argon inlet and drying tube were removed, andthe flask was equipped with a condenser and thermocouple. The reactionmixture was heated to reflux and monitored by TLC (using a 1:2:6MeOH:EtOAc:hexane solvent system). After stirring at reflux for 5 hours,the reaction flask was fitted with a short path distillation apparatusand ethanol was distilled off (70 mL). The resulting residue was cooledto 10° C. and treated dropwise with NaOEt (21 wt %, 37.7 mL, 101.04mmol). The resulting mixture was then treated with N-methylhydroxylaminehydrochloride (3.51 gm; 42.05 mmol). The reaction flask was thenre-equipped with a drying tube and argon inlet, and the reaction wasstirred at ambient temperature.

b) The reaction was allowed to stir for 18 hours at ambient temperature.TLC analysis (using 50% EtOAc in hexane and 10% methanol in CH₂Cl₂)showed completion of the reaction. The reaction flask was placed in anice-water bath, and the reaction mixture was treated dropwise with acooled (ice-water bath) mixture of glacial acetic acid (3.3 mL; 57.4mmol) and 33 mL of distilled water. After completion of the addition ofthe aqueous acetic acid solution, the pH of the mixture was adjusted tobetween 6.4 to 6.8 with 1N NaOH (litmus). The mixture was then treatedwith additional distilled water (5 mL) where upon solid began toprecipitate out. The reaction flask was then equipped with a short pathdistillation apparatus, and approximately 27 mL of solvent was removed(80 mm of Hg vacuum at 30-35° C.). The pH of the resulting mixture wasre-adjusted to between 6.4 to 6.8, and the mixture was allowed to stirwith cooling from an ice-water bath for 30 minutes. The solid wascollected by filtration, and the solid product was washed with ice-colddistilled water. The air-dried product was then placed in a vacuum ovenand dried for 18 hours at 60° C. under vacuum to give 9.51 gm oftepoxalin (87.9% yield, HPLC wt % purity of 98.6%).

EXAMPLE 5

a) An oven-dried 250 mL 3-necked round bottomed flask was equipped withan argon inlet, drying tube, and magnetic stirring bar. A stream of dryargon was supplied, and the flask was charged with4-chloro-γ,ε-dioxo-benzenehexanoic acid (10 gm; 39.27 mmol), p-methoxyphenyl hydrazine hydrochloride (11.32 gm; 42.78 mmol and anhydrousethanol (80 mL, denatured with toluene). The resulting slurry was cooledwith stirring using an ice-water bath. The mixture was treated withpowdered NaOH (1.73 gm; 43.25 mmol). The mixture was stirred at roomtemperature for 14 hours to bring about completion of the reaction(monitor the reaction by thin layer chromatography using 5% MeOH inmethylene chloride developing the plate 4-5 times with U.V. detection).The reaction flask was fitted with a short path distillation apparatus,and solvent was removed under reduced pressure. (A vacuum ofapproximately 40 mm of Hg was used for the vacuum distillation.) Theresidue from the vacuum distillation was azeotropically dried withtoluene (2×40 mL). (A vacuum of approximately 40 mm of Hg was used forthe azeotroping.) Ethanol (66 mL) was added to the residue, and themixture was stirred to produce a fine suspension. The suspension wastreated with concentrated sulfuric acid (0.1 mL; 3.6 meq), and themixture was heated to reflux. The reaction was stirred at reflux for 16hours (the reaction mixture becomes very dark upon the addition of thesulfuric acid). Monitor the reaction by TLC (10% MeOH in methylenechloride). The solvent was then removed under reduced pressure via ashort path distillation apparatus to produce an oily residue. (A vacuumof approximately 40 mm of Hg was used for the vacuum distillation.)

The residue from the vacuum distillation was azeotropically dried withtoluene using a short-path distillation apparatus (2×40 mL). (A vacuumof approximately 40 mm of Hg was used for the azeotroping. The productcrystallized out during the azeotroping process.) The resulting residuewas diluted in ethanol (66 mL), and the mixture was stirred at refluxfor 1 hr. The mixture was cooled to room temperature and then to 50° C.using an ice-water bath- The reaction was treated with N-methylhydroxylamine HCl (4.92 gm; 58.91 mmol) followed immediately with NaOMe(33 mL of a 25 wt % solution; 144.21 mmol) with drop-wise addition viaan oven-dried dropping funnel over 20 minutes with good stirring.

b) The resulting reaction mixture was stirred at room temperature for 16hrs (monitor the reaction with TLC 50% EtOAc in hexane). Solvent wasremoved from the reaction via a short path distillation apparatus underreduced pressure. (A vacuum of approximately 40 mm of Hg was used forthe vacuum distillation). Ethanol (20 mL) was added to the thickreaction mixture to allow stirring. The reaction was cooled to 5° C.using an ice-water bath and a solution of aqueous acetic acid (4.6 mL ofglacial acetic acid; 80.04 mmol, in 66 mL of water) was slowly added.The reaction mixture turned clear, and the mixture was seeded with puretepoxalin. Quenching the reaction with slow addition of the aqueousacetic acid solution with seeding (total addition time approximately 20minutes) was continued. By the end of the addition, solid productprecipitated out. The pH of the reaction was adjusted to between6.8-7.0, and the resulting mixture was warmed to room temperature withstirring. (The pH of the reaction was adjusted from pH 9 to between6.8-7.0 using glacial acetic acid.)

The resulting slurry was stirred at room temperature for 1 hr. andethanol was removed from the reaction at reduced pressure via a shortpath distillation apparatus. (A vacuum of approximately 40 mm of Hg wasused for the vacuum distillation with a maximum temperature of 28° C.being obtained.) The pH of the reaction was adjusted to between 6.8-7.0,and the resulting mixture was stirred for 2 hrs in an ice-water bath.The mixture was filtered through a coarse rated sintered glass funneland the solid was washed with distilled water (5×60 mL). The collectedsolid was air dried, and then the solid was dried under vacuum at 65° C.for 12 hrs to obtain crude tepoxalin (13.09 gm; 86.39% crude yield; HPLCwt % purity of 95.26%) as a brown solid.

c) A 250 mL round-bottomed three necked flask equipped with magneticstirring bar and condenser was charged with crude tepoxalin (12.90 gm).The crude product was treated with EtOAc (50 mL), and the resultingslurry was heated to reflux to produce a clear dark-brown solution. Thehot solution was filtered through celite, and the celite was washed withhot EtOAc (5 mL). (Product crystallized out during filtration.) Thefiltrate was heated to reflux to dissolve product that had crystallizedout, and the mixture was cooled slowly to room temperature. The mixturewas stirred at room temperature for 1.0 hr and then with cooling from anice-water bath for 2 hrs. The resulting solid was collected byfiltration and the product was washed with ice-cold EtOAc (3×13 mL).After air-drying, the product was oven dried at 70° C. for 42 hrs toproduce purified tepoxalin (11.25 gm) as a slightly brown solid (87.21%recovery, >99.9% HPLC wt % purity).

EXAMPLE 6 Preparation of an Alcoholic Solution of N-MethylhydroxylamineHCl

A 500 mL one necked round-bottomed flask was charged with an aqueoussolution of N-methylhydroxylamine HCl (30 mL) and toluene (250 mL). Theflask was fitted with a Dean-Stark trap, and approximately 15 mL ofwater was distilled off. The Dean-Stark trap was replaced with a shortpath distillation apparatus, and the remaining toluene was distilledoff. The resulting residue was then dissolved into anhydrous ethanol(250 mL). ¹H NMR analysis gave a molarity of approximately 0.83 M.

What is claimed:
 1. A process for preparing a compound of the formula I

wherein R₁, R₂, R₃ and R₄ are the same or different and are individuallyselected from the group consisting of hydrogen, lower alkyl, loweralkoxy, amino, acetamido, phenyl, halo, hydroxy, lower alkylsulfonyl,lower alkylthio, nitro, trifluoromethyl, omega-trifluoromethyl loweralkoxy, or where R₁, R₂ or R₃, R₄ taken together with the phenyl groupto which they are attached, form a naphthyl or substituted naphthylgroup; comprising reacting a compound of formula II

wherein R₃ and R₄ are as described above, with succinic anhydride and analkoxide base to form a compound of formula III

wherein R₃ and R₄ are described above, reacting the compound of formulaIII with a compound of formula IV

wherein R₁ and R₂ are as described above, to form a compound of formulaV which is isolated

reacting the compound of formula V with an alcohol to form thecorresponding ester of formula VI

wherein R is lower alkyl, which is isolated and reacting the isolatedester with N-methylhydroxylamine hydrochloride to form the compound offormula I.
 2. A process of claim 1, wherein R₁ and R₂ are independentlyselected from the group consisting of hydrogen, 4 ethoxy, 3,4-dimethoxy,2-methoxy, 4-methoxy, and 4-chloro.
 3. A process of claim 2, wherein R₃and R₄ are independently selected from hydrogen, 4-chloro, 4-methyl,3,4-dimethyl, 2,4,6-trimethyl, 2-methyl, 4-ethyl, 4CF₃, 4-fluoro and4-methoxy.
 4. A process of claim 3, wherein R₁ is 4-methoxy, and R₃ is4-Cl, R₄ is H and R₂ is H.